The magnets which are arranged between two teeth are used to prevent magnetic flux leakages between the magnetic poles in the form of teeth. In fact, it has been found that a substantial part of the magnetic flux created by the winding of the rotor passed via leakage paths instead of passing through the air gap of the machine, and giving rise to the required induction in the poles of the stator. For this purpose, according to solutions of the prior art, magnets are placed preferentially in pairs between at least some of the consecutive teeth of the magnet wheels, either by means of clips or any other support which is arranged on the tooth and is designed to retain at least one magnet in a specific position, or by means of two grooves provided in one of the lateral edges of the teeth between which the magnet is situated.
In the field, there is already known a rotor of a rotary electrical machine, in particular for an alternator or an alternator-starter of a motor vehicle, comprising an axial axis of symmetry X-X, two magnet wheels each comprising a flange supporting projections which are extended by teeth with axial orientation facing towards the flange of the other magnet wheel, a core between the flanges of the magnet wheels, an excitation winding insulator fitted on the core, a winding, and at least one magnet fitted between two adjacent teeth belonging to one and the other of the magnet wheels, wherein the insulator comprises a sleeve fitted on the core, a front cheek and a rear cheek at each of the ends of the hub, at least one of these cheeks supporting a plurality of projecting petals which are designed to cooperate with the inclined inner periphery of a tooth, at least one petal out of the said plurality of petals having a globally trapezoidal contour, the said petal projecting globally radially in the free state whilst being inclined axially in the direction of the second magnet wheel, and having a large base which is connected to the outer periphery of the cheek, and a small base which is configured to come into contact with the said inner periphery of the said tooth, with at least two opposite faces connecting the said large base and small base.
A rotor of a rotary electrical machine of this type is disclosed in WO2011058254.
The assembly method according to teaching derived from WO2011058254 comprises the following steps:
an insulator equipped with an excitation winding is fitted on a half-core of a first magnet wheel;
at least one magnet is fitted on a tooth of the said first magnet wheel;
the said petal is turned back and folded progressively by contact with the inclined inner periphery of the tooth of the second magnet wheel, making the said petal go from a deployed position to a folded position.
By using a method of this type for fitting of a rotor, it has been found that during the fitting step in which the said petal is turned back and folded progressively by contact with the inclined periphery of the tooth of the second magnet wheel, the passage of the said petal from a deployed position to a folded position was made difficult because of the prior fitting of the said magnet on the tooth of the first magnet wheel. During this aforementioned prior fitting, the magnets are simply deposited and retained by magnetisation on the first magnet wheel.
Thus, during the assembly of the second magnet wheel, the petal which is progressively folded towards the excitation winding is liable to draw these magnets with it. The interpolar magnets are then displaced, such that the rotor obtained at the end of the process must be scrapped.
In other words, when the said petal is turned back and folded, there is at least one intermediate position of the petal according to which the said petal is in the immediate vicinity of, or even crosses, a ridge of the said magnet of the first magnet wheel. In this case, intermediate position means the position in which the said petal is on the point of clearing the magnet which equips the first magnet wheel, without having completely cleared it.
This intermediate position is therefore a position between a first position relating to a deployed state of the said petal, and a second position relating to a folded state of the said petal.
As can be seen in FIG. 1 representing a prior art, in the intermediate position the said magnet which equips the first magnet wheel is very close to the said petal, or even touches the said petal. This immediate vicinity affects the production costs. In fact, in these conditions, during the assembly the said magnet can damage the petal by colliding with it.
In order to eliminate this problem, it is possible for example to equip the rotor with petals with reduced dimensions, or even to reduce the size of the magnets.
These solutions are not satisfactory since the first one referred to reduces the electrical insulation of the coil, and the second one assists magnetic leakage paths.